The broad goal of this project, Origins of Communication Disorders in Late Talkers, is to achieve an understanding of the linguistic and non- linguistic factors that are associated with persistent deficits or successful recovery from initial language delay in a population of children who are in the bottom tenth percentile for expressive vocabulary between 18 and 24 months of age. Followup studies in our laboratory and at other research sites demonstrate that approximately 40% of these children qualify for a diagnosis of specific language impairment by 3 - 4 years of age. To uncover the factors associated with early and persistent language delay, we have designed our measures around two periods of development: (1) the earliest stages of language acquisition (18 - 36 months), when accurate determination of language impairment is still difficult to make, and (2) preschool to first grade (3 - 6 years), when diagnosis with standardized tests is possible. Based on pilot studies with a small sample of late talkers, we have developed a series of specific hypotheses concerning (1) intralinguistic factors (e.g. receptive language profiles) that distinguish between "late bloomers" and the truly language impaired during the "preclinical" stage(i.e. 18 - 24 months), and (2) extralinguistic factors (e.g. aspects of symbolic gesture) that also differentiate between these two groups, increasing the validity and reliability of early diagnosis. In addition, we will investigate the shape and nature of recovery from delay in those children who do recover, including (3) cognitive infrastructures, i.e. non- linguistic skills that must be in place before successful recovery can begin, (4) alternative modes of communication (gestural, vocal, facial) that are used by "late bloomers" during their period of delay, compared with the non-linguistic alternatives displayed by children with persistent deficits. For those children who do show apparent recovery according to standardized tests, the 3 - 6 year battery contains a series of more subtle linguistic measures that can be used to determine (5) whether or not the "late bloomers" continue to display subtle deficits in oral language ability that may affect their performance in the school system. Finally, (6) the behavioral profiles obtained in this project will be coordinated with electrophysiological studies of the same children (see Project 5), to determine whether and to what extent changes in linguistic and non-linguistic ability in late talkers can be linked to specific changes in brain organization for language. Results for both groups of late talkers will be compared with the cross-domain profiles and developmental trajectories displayed by other groups under study within the Program Project. In addition to their clinical/diagnostic value, results of all these studies are relevant to fundamental questions about the nature of the language processor: Do the initial delays in language displayed by late talkers reflect temporary and/or persistent deficits in a "language module" that can be dissociated from other mental/neural systems? Or will we find that initial delays and/or recovery from delay are systematically associated with delay and/or recovery in certain non-linguistic domains (e.g. attention, cognition, affect) that are critical for normal language development?